This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We are investigating the accuracy of absolute and relative quantification of proteins in simple and complex mixtures using the 3 highest ionizing peptides. The average of the areas under the curve of the three highest ionizing peptides provides a metric for relative and absolute quantification. In addition we are comparing the HI 3 method with spectral counting